Certain water/alcohol soluble extracts from plant sources have been found to reduce cholesterolemia in chicks, pigs and rats (P. Griminger, et al., "Dietary Saponin and Plasma Cholesterol in the Chick." Proc. Soc. Exp. Biol. Med. 99:424-426, 1958; H. A. I. Newman, et al. "Dietary Saponins, a Factor Which May Reduce Liver and Serum Cholesterol Levels." Poultry Sci. 37:42-46, 1958; B. Morgan, et al., "The Interactions Between Dietary Saponin, Cholesterol and Related Sterols in the Chick." Poultry Sci. 51:677-682, 1972; D. L. Topping, et al., "Effects of Dietary Saponins in Fecal Bile Acids and Neutral Sterols, Plasma Lipids and Lipoprotein Turnover in the Pig." Am. J. Clin. Nutr. 33:783-786, 1980; D. G. Oakenfull, et al., "Effects of Saponins on Bile-acids and Plasma Lipids in the Rat." Br. J. Nutr. 42209-216, 1979; and D. L. Topping, et al., "Prevention of Dietary Hypercholesterolemia in the Rat by Soy Flour High and Low in Saponins." Nutr. Rep. Int. 22:513-519, 1980.)
Among these plant extracts, extracts from alfalfa hay have been shown to be active in reducing the absorption of dietary cholesterol. In particular, these alfalfa extracts reduce the intestinal absorption of cholesterol in rats and monkeys (M. R. Malinow, et al., "Cholesterol and Bile Acid Balance in Macaca fascicularis: Effects of Alfalfa Saponins," J. Clin. Invest. 67:156-162, 1981.) These alfalfa extracts have been shown to contain saponins identifiable by thin-layer chromatography. The alfalfa extracts contain, in addition to saponins, unspecified amounts of carbohydrates, amino acids, peptides, pigments, and free aglycones that are removed from alfalfa hay by the water solvent used during their preparation. The capacity of such alfalfa extracts to interfere with cholesterol absorption is enhanced by partial acid hydrolysis as reported in M. R. Malinow, et al., "Effect of Alfalfa Saponins on Intestinal Cholesterol Absorption in Rats," Am. J. Clin. Nutr. 30:2061-2067, 1977; and U.S. Pat. No. 4,242,502 (Malinow, et al.) herein incorporated by reference.
It was previously reported that the toxicity of plant saponins is decreased in rats, mice, and birds of by cholesterol in the diet (J. O. Anderson, "Effect of Alfalfa Saponin on the Performance of Chicks and Laying Hens." Poult. Sci. 36:873-876, 1957; I. Ishaaya, et al., "Soybean Saponins. IX. Studies of Their Effects on Birds, Mammals and Cold-blooded Organisms." J. Sci. Food Agric. 20:433-436, 1969; G. Reshef, et al., "Effect of Alfalfa Saponins on the Growth and Some Aspects of Lipid Metabolism of Mice and Quails." J. Sci. Food Agric. 27:63-72, 1976; E.G. Wilcox, et al., "Serum and Liver Cholesterol, Total Lipids and Lipid Phosphorus Levels of Rats Under Various Dietary Regimes." Am. J. Clin. Nutr. 9:236-243, 1961.
Despite these encouraging results, it remained a problem that plant extracts, which are of variable composition, contain a volume of nonuseful chemical substances. It is difficult, due to the variations in composition, to set a standard dosage or predict the impurities present. Thus, such extracts are not well suited for use by humans.
Subsequently, and as set forth in U.S. Pat. No. 4,602,003 (Malinow) and U.S. Pat. No. 4,602,005 (Malinow), which are herein incorporated by reference, it was discovered that certain synthetically produced, pure "sapogenin-derived" compounds, e.g., substances compounded from spirostane, spirostene, or sterol-derived compounds, are nontoxic. Specifically, U.S. Pat. Nos. 4,602,003 and 4,602,005 disclose the use of glycosides having a tigogenin or diosgenin aglycone moiety, such as tigogenin cellobioside, for the treatment of hypercholesterolemia and atherosclerosis. Such compounds were shown to depress cholesterol absorption more effectively than alfalfa extracts on a weight basis and thus can be administered in reasonably sized doses. Because the chemical compositions of these substances are known and because they can be synthesized at a high degree of purity, they can be used to treat any warm-blooded animal, including humans. However, the synthesis of these compounds, as set forth in U.S. Pat. No. 4,602,003, is complex, expensive and requires the use of large quantities of environmentally hazardous organic solvents such as chloroform, acetic acid and methanol and heavy metals such as silver or mercury.
Moreover, currently the only known commercially available source of the starting compound, tigogenin, is the plant Agave sisalane. This plant is grown commercially only in mainland China and Mexico and takes seven years to grow to maturity. Diosgenin can be obtained from several dioscoracaeae plants that are grown in Mexico.